Filter for improving the electromagnetic compatibility of components of an electric drive of a vehicle

ABSTRACT

A damping device is designed to dampen noise signals in a cable having a plurality of wires. The damping device includes a plurality of first terminals, to which is applied the voltage vector U1 and where the current vector I1 flows, a wire of the cable being connected to each first terminal; a plurality of second terminals, to which is applied the voltage vector U2 and where the current vector h flows, a wire of the cable being connected to each second terminal; and a first plurality of dipoles, whose first terminal is connected to the wire k and whose second terminal is connected to ground.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No.PCT/EP2015/072813, filed Oct. 2, 2015, which claims priority under 35U.S.C. § 119 from German Patent Application No. 10 2014 222 363.6, filedNov. 3, 2014, the entire disclosures of which are herein expresslyincorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The present application relates to an improved damping device whichimproves the electromagnetic compatibility of components of anelectrically driven vehicle.

Electric drives can be used in a vehicle with a hybrid drive or with anexclusively electric drive. In the case of an electric drive, theelectromagnetic compatibility (EMC) must be ensured so that othercomponents inside and outside the vehicle are not disrupted.

The measures known from the prior art for improving the electromagneticcompatibility for high-voltage networks in a vehicle with an electricdrive are not satisfactory. A conventional EMC filter serves primarilyto damp interference signals which are emitted by an active electricaldevice, for example an inverter, a DC/DC converter and the like. That isto say the function of the filter is to damp a source of interference.In addition to filtered and damped power electronics, a motor vehiclecontains further sources of interference which do not always satisfy therequirements of the CE standard. Therefore, in a motor vehicle there maybe interference even though the power electronics do not generate anyemissions. The resonances in connecting structures, in particular in thecable harnesses, amplify the emissions at certain frequencies. In someconfigurations, this effect can be significant since the resonances inthe connecting structures can cause an interference signal to beradiated by the entire motor vehicle.

Conventional EMC filters do not damp any cable harness resonances whichare external with respect to an electrical device.

EP 0 274 347 A1 discloses a series circuit of a resistor and of acapacitor which are each connected between a line and ground.

DE 196 36 816 A1 discloses a ferrite reactor, and discloses that linesare connected to ground via a series circuit composed of a resistor anda capacitor, in order to adapt the wave impedance.

The invention has the object of providing an improved damping device andan improved method for configuring a damping device.

The object of the invention is achieved by a damping device, a motorvehicle having such a damping device, as well as a method of operatingthe damping device, in accordance with embodiments of the invention.

A damping device according to the invention is designed to dampinterference signals in a cable having a plurality of wires andcomprises a plurality of first terminals to which the voltage vector U₁is applied and at which the current vector I₁ flows, wherein a wire ofthe cable harness is connected to every first terminal, and a pluralityof second terminals to which the voltage vector U₂ is applied and atwhich the current vector I₂ flows, wherein a wire of the cable harnessis connected to each second terminal. The damping device comprises afirst plurality of dipoles Z_(kk) whose first terminal is connected tothe wire k and whose second terminal is connected to ground, andoptionally a second plurality of dipoles Z_(km) whose first terminal isconnected to the wire k and whose second terminal is connected to thewire m.

The following applies:

${\overset{\overset{\_}{\_}}{A} = \begin{pmatrix}{\overset{\overset{\_}{\_}}{A}}_{11} & {\overset{\overset{\_}{\_}}{A}}_{12} \\{\overset{\overset{\_}{\_}}{A}}_{21} & {\overset{\overset{\_}{\_}}{A}}_{22}\end{pmatrix}},$where the following applies

${\begin{pmatrix}\overset{\_}{U_{1}} \\\overset{\_}{I_{1}}\end{pmatrix} = {\begin{pmatrix}{\overset{\overset{\_}{\_}}{A}}_{11} & {\overset{\overset{\_}{\_}}{A}}_{12} \\{\overset{\overset{\_}{\_}}{A}}_{21} & {\overset{\overset{\_}{\_}}{A}}_{22}\end{pmatrix} \cdot \begin{pmatrix}\overset{\_}{U_{2}} \\\overset{\_}{I_{2}}\end{pmatrix}}};$${{\overset{\overset{\_}{\_}}{Y}}_{w} = {\sqrt{{\overset{\overset{\_}{\_}}{A}}_{21}{\overset{\overset{\_}{\_}}{A}}_{12}^{- 1}} = \left\{ y_{km} \right\}}},k,{{m = \overset{\_}{1,n}};}$the admittance matrix, and;

Y _(w) the admittance matrix, and;

A is the chain matrix of the cable.

The resistance and the reactance of the dipoles Z_(km), Z_(kk) aredetermined as follows:

$Z_{k,m} = \left\{ \begin{matrix}{{- \frac{1}{y_{k,m}}},{k \neq m},} \\{{1/{\sum\limits_{i = {1:n}}^{\;}\; y_{k,i}}},{k = {m.}}}\end{matrix} \right.$

The cable can be a cable harness, for example a cable harness of anelectrically driven motor vehicle. The damping device has the topologyof an impedance matrix with a capacitive and an inductive isolation inthe lower frequency range which serves to avoid interference with afunction in the lower frequency range. The entire circuit of the dampingdevice comprises N!/(2×(N−2)! modal wave impedances which are connectedbetween preferably all the cable wires and all the cable shield sleeves,but a large part of these impedances can be reduced or eliminated, sincenot all the resonance modes have to be damped.

One of the wires of the cable can be a first shield which shields atleast one other wire. The first shield can be connected to ground via adipole Z_(kk), and the wires of the cable can each be connected to thefirst shield via a dipole Z_(km). In another embodiment, the firstshield can be connected to a second shield via a dipole Z_(kk) and thewires of the cable can each be connected to the first shield via adipole Z_(km). The electromagnetic behavior of the cable and of theelectrical devices connected thereto can be improved by the shields andthe shielding of individual wires or of a plurality of wires by means ofa shield. The damping device can have an inductance which is connectedto a wire of the cable. In particular, the inductance can be connectedin series with the wire. Alternatively or additionally, the dampingdevice can have a component which acts as an inductance, for example anSMD ferrite or a CM core, and is arranged around a plurality of wires ofthe cable. Alternatively to this or in addition, the damping devicecomprises a component which acts as an inductance and is arranged aroundall the wires of the cable apart from the second shield.

If the modal wave impedances are greater than or comparable to inputimpedances, SMD ferrites or CM/DM ferrite cores can be used for theinductive isolation. This ensures that the input impedances which areconnected in parallel cannot influence the damping of the resonance. Theselection of a specific isolation measure depends on the different typesof filter and on the EMC filter concept which is used.

The invention also relates to a motor vehicle having an electric driveand the damping device described above.

The first shield can be a cable harness ground, and the second shieldcan be a housing shield which is connected to the bodywork.

In another embodiment, the dipoles Z_(kk) can be connected to the firstshield and each wire can be coupled to the first shield by means of asecond capacitance, wherein in every wire an inductance is connectedbetween the dipole and the second capacitance. This type of wave dampingis advantageous, in particular, in the case of a low-voltage signalcable harness.

In comparison with the wave impedances in the frequency range in whichthe cable resonances take place, the inductance preferably has a highresistance, and the capacitor preferably has a low resistance.

The invention also relates to a method for determining the resistanceand the reactance of dipoles (Z_(km), Z_(kk)) of a damping device for acable having a plurality of wires, wherein the damping device has aplurality of first terminals to which the voltage vector U₁ is appliedand at which the current vector I₁ flows, wherein a wire of the cableharness is connected to every first terminal, a plurality of secondterminals to which the voltage vector U₂ is applied and at which thecurrent vector I₂ flows, wherein a wire of the cable harness isconnected to every second terminal, a first plurality of dipoles Z_(kk)whose first terminal is connected to the wire k and whose secondterminal is connected to ground, and an optional second plurality ofdipoles Z_(km) whose first terminal is connected to the wire k and whosesecond terminal is connected to the wire m.

The expression ground within the scope of this patent application alsocomprises a local ground, for example a housing ground or a shieldground or a housing shield ground.

The method comprises the step of determining the S parameters of thecable by way of a measurement or a computer-implemented calculation orsimulation. S parameters can include the control parameters. The chainmatrix A can be calculated from the S parameters. The S parameters canbe determined by a commercially available network analyzer. The Sparameter matrix can be converted into a chain matrix A by formulaswhich are known to a person skilled in the art. The following applies:

${\overset{\overset{\_}{\_}}{A} = {{\begin{pmatrix}{\overset{\overset{\_}{\_}}{A}}_{11} & {\overset{\overset{\_}{\_}}{A}}_{12} \\{\overset{\overset{\_}{\_}}{A}}_{21} & {\overset{\overset{\_}{\_}}{A}}_{22}\end{pmatrix}\mspace{14mu}{{and}\begin{pmatrix}\overset{\_}{U_{1}} \\\overset{\_}{I_{1}}\end{pmatrix}}} = {\begin{pmatrix}{\overset{\overset{\_}{\_}}{A}}_{11} & {\overset{\overset{\_}{\_}}{A}}_{12} \\{\overset{\overset{\_}{\_}}{A}}_{21} & {\overset{\overset{\_}{\_}}{A}}_{22}\end{pmatrix} \cdot \begin{pmatrix}\overset{\_}{U_{2}} \\\overset{\_}{I_{2}}\end{pmatrix}}}};$The admittance matrix Y is determined by the following equation:Y _(w)√{square root over (A ₂₁ A ₁₂ ⁻¹)}={y_(km)}, k,m=l, n;where A ₂₁ has as a unit an impedance and A ₂₁ has as a unit theadmittance, which are each extracted from the chain matrix, and Y _(w)is a modal admittance matrix. The resistance and the reactance of thedipoles Z_(km), Z_(kk) can be determined by the following equations:

$Z_{k,m} = \left\{ \begin{matrix}{{- \frac{1}{y_{k,m}}},{k \neq m},} \\{{1/{\sum\limits_{i = {1:n}}^{\;}\; y_{k,i}}},{k = {m.}}}\end{matrix} \right.$

The approaches to damping common-mode resonances and differential-moderesonances for networks or cables known in the prior art are based on ascalar formulation of the wave impedances without taking into accountthe intermediate effects of the impedances owing to a parallelconnection of common-mode impedances and differential-mode impedances.The circuits used in the prior art do not form an entire matrix andcannot damp all the resonance modes. The inventor has recognized thatthis problem can be solved by modal formulation of the wave impedancewhich can be represented as a network.

The damping device which is disclosed can take into account theresonances and the modes of a cable or of a cable harness and ensuresthat the cable or the cable harness emits or receives less interference.The damping devices of the prior art have hitherto merely taken intoaccount the properties of an electrical device that was damped, but havenot sufficiently taken into account the cable harness or the cable.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of one ormore preferred embodiments when considered in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system circuit diagram of an electrical device with respectto the damping of interference signals.

FIG. 2 is a general structure diagram of a modal wave damper.

FIG. 3 shows a section through a high-voltage direct current line.

FIG. 4 shows a schematic plan view of a high-voltage direct currentline.

FIG. 5 is a circuit diagram of a damping device for a high-voltagedirect current line.

FIG. 6A shows a first diagram with interference voltages.

FIG. 6B shows a second diagram with interference voltages.

FIG. 7 is a schematic section diagram through a high-voltage alternatingcurrent line of a vehicle with an electric drive.

FIG. 8 is an exemplary routing of a cable in a vehicle.

FIG. 9 is a circuit diagram of a damping device for a three-wirehigh-voltage line.

FIG. 10 is a graph showing interference voltages in the case of athree-wire high-voltage line.

FIG. 11 shows a damping device in the case of a low-voltage signal cableharness.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is made to FIG. 1 which shows a system circuit diagram of anelectrical device with respect to the damping of interference signals.The electrical device 1 has an EMC filter 2 which is connected to ground8 and to N wires of a cable harness 6. An inventive damping device 4 isconnected between the EMC filter 2 and the cable harness 6. The EMCfilter 2 is designed to damp the electrical device 1 toward the inside.Consequently, properties of the electrical device 1 are taken intoaccount in the design of the EMC filter 2. The damping device 4 isdesigned to damp the electrical device 1 toward the outside.Consequently, properties of the surroundings of the electrical device 1,for example of the cable harness 6, are taken into account in the designof the damping device 4.

FIG. 2 shows a general embodiment of a damping device 100 according tothe invention. A cable 102 with a plurality of wires 1 to N is connectedto the damping device 100. A first plurality of dipoles Z₁₁, Z₂₂ andZ_(NN) is connected from one wire in each case to ground. A secondplurality of dipoles Z₁₂, Z_(1N) and Z_(2N) is connected from wire towire. An inductive isolator device 104, which can have, for example, SMDferrites, is also connected into the cable 102. The actual electricaldevice 110 is connected to the inductive isolator device 104. The valuesof the dipoles Z_(km) and Z_(kk) are calculated by determining thescatter parameters (S parameters) by way, for example, of a networkanalyzer. The scatter parameters of the cable can also be determined bya computer-assisted simulation.

A chain matrix (A parameter) is used to calculate the real and complexresistances of the dipoles Z:

${{\overset{\overset{\_}{\_}}{A} = \begin{pmatrix}{\overset{\overset{\_}{\_}}{A}}_{11} & {\overset{\overset{\_}{\_}}{A}}_{12} \\{\overset{\overset{\_}{\_}}{A}}_{21} & {\overset{\overset{\_}{\_}}{A}}_{22}\end{pmatrix}}\;,}\;$where the following applies

${\begin{pmatrix}\overset{\_}{U_{1}} \\\overset{\_}{I_{1}}\end{pmatrix} = {\begin{pmatrix}{\overset{\overset{\_}{\_}}{A}}_{11} & {\overset{\overset{\_}{\_}}{A}}_{12} \\{\overset{\overset{\_}{\_}}{A}}_{21} & {\overset{\overset{\_}{\_}}{A}}_{22}\end{pmatrix} \cdot \begin{pmatrix}\overset{\_}{U_{2}} \\\overset{\_}{I_{2}}\end{pmatrix}}};{and}$${{\overset{\overset{\_}{\_}}{Y}}_{w} = {\sqrt{{\overset{\overset{\_}{\_}}{A}}_{21}{\overset{\overset{\_}{\_}}{A}}_{12}^{- 1}} = \left\{ y_{km} \right\}}},k,{m = {\overset{\_}{1,n}.}}$

The values of the dipoles Z_(km) and of the dipoles Z_(kk) can becalculated as follows:

$Z_{k,m} = \left\{ \begin{matrix}{{- \frac{1}{y_{k,m}}},{k \neq m},} \\{{1/{\sum\limits_{i = {1:n}}^{\;}\; y_{k,i}}},{k = {m.}}}\end{matrix} \right.$

The S parameters are determined, as was mentioned above, by use of avector network analyzer. The term y_(M) denotes elements of the modalimpedance matrix Y_(w). As has been mentioned above, the matrix A ₂₁ hasthe impedance as a unit, and the matrix A ₂₁ has the admittance as aunit. The dipoles Z_(km), Z_(kk) are to be used only if the modal waveimpedances are lower than or in the region of the input impedances, forexample in the case of an IC input or a cable shield against a cablesleeve. If the modal wave impedances are greater than or in the regionof the input impedances, inductive isolation must be provided by way ofan inductance, for example an SMD ferrite or acommon-mode/differential-mode ferrite core. This ensures that the inputimpedances which are connected in parallel cannot influence the dampingof the resonance.

Reference is made to FIGS. 3, 4 and 5 which show a damping device 200for a high-voltage DC line 202, with FIG. 3 showing a cross sectionthrough a first line element 204 and a second line element 206 of thehigh-voltage DC line 202, FIG. 4 showing a plan view of the high-voltageDC line 202, and FIG. 5 showing the damping device 200.

The damping device 200 for the high-voltage DC line 202 is an importantelement of the entire filter topology which damps resonances in atraction network. The high-voltage DC line 202 comprises two lineelements 204, 206 each with a wire 214, 224. Since the shield sleeves208, 216 are connected by plugs 226, 228, the high-voltage DC line 202can be described as a 3×3 matrix of modal wave impedances. In the caseof a high-voltage DC line, the wave impedance matrix does not have to befully occupied in order to determine the values of the dipoles of thedamping device 200 because a low differential impedance of anintermediate circuit capacitor on the power electronics side or theimpedance of the cells of a high-voltage accumulator can only be avoidedwith difficulty. Nevertheless, it is possible with the approachaccording to the invention to damp all three common-mode resonance modes(total system resonances) efficiently. It goes without saying that thiscalculation has to be carried out separately for each cable model and/orfor each type of routing in the vehicle.

A plug 226 is connected to a power electronics device 260. A first wire214 and a second wire 224 are connected to the plug 226. The wires 214and 224 are connected to a battery 250 via a ferrite core 232 and aconventional high-voltage filter 240. The high-voltage DC line 202comprises an environmental insulation sleeve 208, an individual shield210, an insulator element 212 and the wire 214, for example with a crosssection of 35 mm2. The ferrite core 232 surrounds all the lines andgenerates impedances of approximately 300 Ωat a frequency ofapproximately 10 MHz up to approximately 30 MHz.

The first wire 214 is connected to a cable harness shield ground 210,218 via a capacitor C₁₃ and a resistor R₁₃ connected in series. Thesecond wire 224 is connected to the cable harness shield ground 210, 218via a capacitor C₂₃ and a resistor R₃₂ connected in series. The cableharness shield ground is connected to the high-voltage filter 240 viathe ferrite core 232.

The cable harness shield ground 210, 218 is also connected to the plug226. The cable harness shield ground 210, 218 can consequently beconsidered to be a wire of the cable 202. The cable harness shieldground 210, 218 is connected to the housing shield ground 230 via acapacitor C₃₃ and a resistor R₃₃. The housing shield ground 230 isconnected to the high-voltage filter 240 via the housing ground 228, andto the cable harness shield ground 210, 218 via the ferrite core 232.The housing shield ground is connected via a cable 236 to the bodywork234 which forms the actual ground of the vehicle.

The scatter matrix for the line 202 is constructed as follows:

−10.1560 −3.9032 −3.7713 −12.9042 −32.0056 −24.7212 −3.9032 −10.1560−3.7713 −32.0056 −12.9042 −24.7212 −3.7713 −3.7713 −9.0316 −24.7212−24.7212 −16.8940 −12.9042 −32.0056 −24.7212 −10.1560 −3.9032 −3.7713−32.0056 −12.9042 −24.7212 −3.9032 −10.1560 −3.7713 −24.7212 −24.7212−16.8940 −3.7713 −3.7713 −9.0316 Unit: dB

As a result, the following values are obtained for the resistances andcapacitances:

R₁₃=R₂₃ ₌7 Ω, R₃₃=122 Ω, C₁₃=C₂₃=C₃₃=10 nF, where the admittance matrixhas the following values:

0.1532 0.0000 −0.1532 0.0000 0.1532 −0.1532 −0.1532 −0.1532 0.3142

Reference is made to FIGS. 6A and 6B, where FIG. 6A hasdifferential-mode interference voltages and FIG. 6B has common-modeinterference voltages. The frequency is plotted on the abscissa, and thevoltage level on the ordinate in dB. The curve 264 shows thedifferential-mode interference signal without filtering. The curve 264shows the differential-mode interference signal if only the conventionalhigh-voltage filter 240 according to the prior art is used to damp thedifferential-mode interference signal 262. The curve 266 shows theremaining differential-mode interference signal if both the conventionalhigh-voltage filter 240 and the damping device 200 according to theinvention are used.

The curve 268 shows the level of the common-mode interference withoutdamping. The curve 270 shows the level of the common-mode inference ifonly the conventional high-voltage filter 240 according to the prior artis used. The curve 272 shows the remaining common-mode interference ifboth the conventional high-voltage filter 240 and the damping deviceaccording to the invention are used to damp the common-modeinterference.

These exemplary measurements have been determined in a line between abattery 250 and an inverter 260. The common-mode interferences and thedifferential-mode interferences have a plurality of resonances as aresult of circuits in the lower frequency range and a plurality ofhousing resonances and cable harness resonances at frequencies higherthan 20 MHz. The damping device 200 according to the invention damps themodes effectively without changing the resonance behavior of the cable.The common-mode interference can be reduced by up to 50 decibels.

Reference is made to FIGS. 7, 8 and 9 which show a three-wirehigh-voltage line, with FIG. 7 showing a section through the three-wirehigh-voltage line 301, FIG. 8 showing the routing of the three-wirecable 301, and FIG. 9 showing a connection of the damping device 300according to the invention. The high-voltage line 301 comprises threewires U, V, W, around each of which an insulator element 302 isarranged. The three lines U, V, W are twisted with one another andembedded in a plastic 304. A shield 305 is arranged around the plastic.It goes without saying that a further insulation layer can be providedoutside the cable harness shield 305. FIG. 8 shows exemplary routing ofthe high-voltage line from an inverter 320 to an electric machine 322.

The high-voltage line 301 from the electric machine 322 is connected toa plug 306. The wire U is connected via a series circuit of a capacitorC₁₄ and a resistor R₁₄ to a cable harness shield ground 310 which isconnected to the cable harness shield 305 via the plug 306. The wire Vis connected to the cable harness shield ground 310 via a series circuitcomposed of a capacitor C₂₄ and a resistor R₂₄. The wire W is connectedto the cable harness shield ground 310 via a capacitor C₃₄ and aresistor R₃₄. The cable harness shield ground 310 forms a wire. Thewires U, V, W and the cable harness shield 310 are damped by a ferritecore 308. The cable harness shield ground 310 is connected to thehousing shield 314 via a series circuit composed of a capacitor C₄₄ anda resistor R₄₄. The housing shield is connected to the cable harnessshield ground 310 via a housing ground 312 and the ferrite core 308. Thehousing shield ground 314 is connected via a cable 318 to the bodywork316 which forms the actual ground of the vehicle.

The damping device 300 for a high voltage AC line is also an importantdevice of the total filter topology which damps the resonances in linesleading to an electric machine or a high-voltage starter. The approachis suitable for all three-wire cable types. The high-voltage AC line 301comprises three phase conductors U, V, W and a cable harness shield 305as a collective shield. The high-voltage AC line can be described with a4×4 matrix with modal wave impedances. Since the shield cross section isnot constant and the high-voltage AC cable 301 is laid in a complexfashion in the vehicle, such a line is non-homogeneous, i.e. theinterference behavior cannot be generalized. Nevertheless, the scattermatrix can be determined by means of a network analyzer. In particularthe common-mode current damping is relevant for such a high-voltage ACline 301. Consequently, the scatter matrix comprises merely four waveimpedances based on the common-mode interference.

The scatter matrix S has the following values:

−1.4331 10¹ −7.9633 −7.9641 −1.5401 10¹ −2.8268 −2.8111 10¹ −2.8110 10¹−1.7536 10¹ −7.9633 −1.2335 10¹ −8.0873 −1.4407 10¹ −2.7142 10¹ −3.0207−2.8185 10¹ −1.8109 10¹ −7.9641 −8.0873 −1.2338 10¹   1.4408 10¹ −2.714610¹ −2.8190 10¹ −3.0201 −1.8108 10¹ −1.5401 10¹ −1.4407 10¹ −1.4408 10¹−2.8043 −2.6129 10¹ −3.2101 10¹ −3.2089 10¹ −4.4930 −2.8268 −2.8111 10¹−2.8110 10¹ −1.7536 10¹ −1.3525 10¹ −8.3955 −8.3964 −1.1819 10¹ −2.714210¹ −3.0207 −2.8185 10¹ −1.8109 10¹ −8.3955 −1.1748 10¹ −8.5136 −1.141010¹ −2.7146 10¹ −2.8190 10¹ −3.0201 −1.8108 10¹ −8.3964 −8.5136 −1.175010¹ −1.1410 10¹ −2.6129 10¹ −3.2101 10¹ −3.2089 10¹ −4.4930 −1.1819 10¹−1.1410 10¹ −1.1410 10¹ −4.5351 Unit: dB

With the circuit shown in FIG. 9 the following values are obtained:

R₁₄=55 Ω, R₂₄=55 Ω, R₃₄=63 Ω, R₄₄=18 Ω, C₁₄=C₂₄=C₃₄ is=100 pF, C₄₄=10nF;

wherein the wave admittance matrix has the following values:

3.8423 10⁻² −1.5343 10⁻² −1.5340 10⁻² −6.0786 10⁻³ −1.5182 10⁻² 4.259710⁻² −1.5676 10⁻² −1.0918 10⁻² −1.5179 10⁻² −1.5675 10⁻² 4.2591 10⁻²−1.0915 10⁻² −9.6681 10⁻³ −1.3501 10⁻² −1.3496 10⁻² 8.5735 10⁻²

The AC dielectric strength is a critical problem in the case ofhigh-voltage AC filtering. Customary capacitors which are used forelectromagnetic compatibility and which have a capacitance of more than1 nF are problematic in the case of voltages of over 400 V and in afrequency range from approximately 800 Hz to approximately 1500 Hz,which are typical values in a vehicle inverter 320. In addition, suchcapacitors with a capacitance in the pF range are not effective whenfiltering. Since the damping effect in the present invention is achievedmainly or only by means of the resistances, capacitors with a lowcapacitance can be used without reducing the damping effect.

Reference is made to FIG. 10 which shows a diagram of interferencesignals. The frequency is plotted on the abscissa. The level of theinterference spectrum is plotted in dBuV on the ordinate. The curve 350shows the input interference spectrum at the power transistors which maybe, for example, IGBT. The curve 352 shows the interference voltage onthe housing of the electric machine 322 without damping. The lineresonances of the wires U, V, W can be clearly seen. In particular, theshield conductor resonance at approximately 28 MHz is problematic, saidshield conductor resonance giving rise to relatively high longitudinalimpedance in the cable shield. The curve 354 shows the common-modeinterference after it has been damped by means of the damping device 300according to the invention.

The present invention can also be applied to a high-voltage common-modeline or a three-phase high-voltage AC line with double shielding. Inthis case, each shield forms a wire in the sense of the calculation bymeans of the scatter parameters and the chain matrix. Likewise, theinvention can be applied for a damping device for a high-voltage DC linewith individual shielding of both wires in one shield. It goes withoutsaying that the invention can also be applied in a damping device for anAC charging device.

Reference is made to FIG. 11 which shows a further embodiment of theinvention. A low-voltage signal cable 420 is damped with the dampingdevice 400 shown in FIG. 11. The low-voltage signal cable can be a cableharness with N wires. A series circuit composed of a capacitor C₁₁ and aresistor R₁₁, also connected to a housing ground 406, is connected tothe first wire of the low-voltage signal cable. A second series circuitcomposed of a capacitor C₂₂ and a resistor R₂₂ is connected between thesecond wire of the low-voltage signal cable and the housing ground 406.A further series circuit composed of a capacitor C_(NN) and a resistorR_(NN) is connected to the wire N of the low-voltage signal cable 402and to the housing ground 406.

A damping inductance 404, which can be, for example, an SMD ferrite, isconnected into each wire. The first input of the inductance 404 in thefirst wire of the low-voltate signal cable is connected to the capacitorC₁₁, and the second terminal of this inductance 404 is connected to acapacitor C_(y1), the other terminal of which is connected to thehousing ground 406. The first terminal of the inductance 404 in thesecond wire of the low-voltage signal cable 402 is connected to acapacitor C₂₂, and the second terminal of the inductance 404 isconnected to a capacitor C_(y2), the other terminal of which isconnected to the housing ground 406. The first terminal of theinductance 404 in the wire N is connected to a capacitor C_(NN), and thesecond terminal of this inductance is connected to a capacitor C_(yN),the other terminal of which is connected to the housing ground 406. Thehousing ground 406 is connected to the housing shield 408, wherein thehousing shield 408 is connected via a cable to the bodywork 412 whichforms the actual ground of the motor vehicle.

This embodiment of the damping device 400 is suitable for cases in whichthe resonances in the low-voltage signal cable 402 are critical for theentire vehicle. The modal wave impedances of the low-voltage signalcable 402 to the bodywork (R_(kk), k=1:N) eliminate all the common-moderesonances. If some differential-mode resonances are known between thewire pairs, these differential-mode resonances can be eliminated bymeans of additional modal impedances. The inductances 404 between thewave damping device, which are formed by the series circuit composed ofcapacitor C_(kk) and resistor R_(kk), and the EMC filter which is formedby the capacitors C_(y), serve for high-frequency damping.

The invention provides an improved damping device for a motor vehicle,since it also takes into account the properties of the cable and of thecable harness.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

What is claimed is:
 1. A damping device to damp interference signals ina cable having a plurality of wires, comprising: a plurality of firstterminals to which a voltage vector U₁ is applied and at which a currentvector I₁ flows, wherein a wire of the cable is connected to every firstterminal; a plurality of second terminals to which a voltage vector U₂is applied and at which a current vector I₂ flows, wherein a wire of thecable is connected to every second terminal; and a first plurality ofdipoles whose first terminal is connected to a wire k and whose secondterminal is connected to ground, wherein the following applies:$\begin{matrix}{{\overset{\overset{\_}{\_}}{A} = \begin{pmatrix}{\overset{\overset{\_}{\_}}{A}}_{11} & {\overset{\overset{\_}{\_}}{A}}_{12} \\{\overset{\overset{\_}{\_}}{A}}_{21} & {\overset{\overset{\_}{\_}}{A}}_{22}\end{pmatrix}}\;,} & (I) \\{{\begin{pmatrix}\overset{\_}{U_{1}} \\\overset{\_}{I_{1}}\end{pmatrix} = {\begin{pmatrix}{\overset{\overset{\_}{\_}}{A}}_{11} & {\overset{\overset{\_}{\_}}{A}}_{12} \\{\overset{\overset{\_}{\_}}{A}}_{21} & {\overset{\overset{\_}{\_}}{A}}_{22}\end{pmatrix} \cdot \begin{pmatrix}\overset{\_}{U_{2}} \\\overset{\_}{I_{2}}\end{pmatrix}}};} & ({II}) \\{{{\overset{\overset{\_}{\_}}{Y}}_{w} = {\sqrt{{\overset{\overset{\_}{\_}}{A}}_{21}{\overset{\overset{\_}{\_}}{A}}_{12}^{- 1}} = \left\{ y_{km} \right\}}},k,{{m = \overset{\_}{1,n}};}} & ({III})\end{matrix}$ wherein A is a chain matrix of an entirety of the cable, Y_(w) is an admittance matrix of the entirety of the cable, and aresistance and a reactance of the dipoles are determined as follows:$\begin{matrix}{Z_{k,m} = \left\{ \begin{matrix}{{- \frac{1}{y_{k,m}}},{k \neq m},} \\{{1/{\sum\limits_{i = {1:n}}^{\;}\; y_{k,i}}},{k = {m.}}}\end{matrix} \right.} & ({IV})\end{matrix}$
 2. The damping device according to claim 1, furthercomprising: a second plurality of dipoles whose first terminal isconnected to the wire k and whose second terminal is connected to a wirem.
 3. The damping device according to claim 1, wherein a wire is a firstshield which shields at least one other wire.
 4. The damping deviceaccording to claim 3, wherein the first shield is connected to groundvia a dipole (Z_(kk)), and the wires of the cable are each connected tothe first shield via a dipole (Z_(km)) or, the first shield is connectedto a second shield via a dipole (Z_(kk)) and the wires of the cable areeach connected to the first shield via a dipole (Z_(km)).
 5. The dampingdevice according to claim 1, wherein the dipole has a real resistanceand a capacitance.
 6. The damping device according to claim 4, whereinthe damping device comprises at least one of: at least one inductancewhich is connected to a wire; at least one component which acts as aninductance and is arranged around a plurality of wires of the cable; andat least one component which acts as an inductance and is arrangedaround all the wires of the cable apart from the second shield.
 7. Amotor vehicle, comprising: an electric drive; and the damping deviceaccording to claim
 4. 8. The motor vehicle according to claim 7, whereinthe first shield is a cable harness ground, and the second shield is ahousing shield which is connected to a bodywork of the vehicle.
 9. Themotor vehicle according to claim 8, wherein the dipoles (Z_(kk)) areconnected to the first shield and each wire is coupled to the firstshield by a second capacitance (C_(y)), wherein in each wire aninductance is connected between the dipole and the second capacitance(C_(y)).
 10. The motor vehicle according to claim 7, wherein the dipoles(Z_(kk)) are connected to the first shield and each wire is coupled tothe first shield by a second capacitance (C_(y)), wherein in each wirean inductance is connected between the dipole and the second capacitance(C_(y)).
 11. A method for determining a resistance and a reactance ofdipoles (Z_(km), Z_(kk)) of a damping device for a cable having aplurality of wires, wherein the damping device comprises: a plurality offirst terminals to which a voltage vector U₁ is applied and at which acurrent vector I₁ flows, wherein a wire of the cable is connected toevery first terminal; a plurality of second terminals to which a voltagevector U₂ is applied and at which a current vector I₂ flows, wherein awire of the cable is connected to every second terminal; a firstplurality of dipoles (Z_(kk)) whose first terminal is connected to awire k and whose second terminal is connected to ground; an optionalsecond plurality of dipoles (Z_(km)) whose first terminal is connectedto the wire k and whose second terminal is connected to a wire m; themethod comprising the steps of: determining S parameters of an entiretyof the cable by a measurement or a computer-implemented calculation;determining a chain matrix A of the entirety of the cable from the Sparameters, where the following applies: $\begin{matrix}{{\overset{\overset{\_}{\_}}{A} = \begin{pmatrix}{\overset{\overset{\_}{\_}}{A}}_{11} & {\overset{\overset{\_}{\_}}{A}}_{12} \\{\overset{\overset{\_}{\_}}{A}}_{21} & {\overset{\overset{\_}{\_}}{A}}_{22}\end{pmatrix}}\;,\mspace{25mu}\text{and}} & (I) \\{{{\begin{pmatrix}\overset{\_}{U_{1}} \\\overset{\_}{I_{1}}\end{pmatrix} = {\begin{pmatrix}{\overset{\overset{\_}{\_}}{A}}_{11} & {\overset{\overset{\_}{\_}}{A}}_{12} \\{\overset{\overset{\_}{\_}}{A}}_{21} & {\overset{\overset{\_}{\_}}{A}}_{22}\end{pmatrix} \cdot \begin{pmatrix}\overset{\_}{U_{2}} \\\overset{\_}{I_{2}}\end{pmatrix}}};}\;} & ({II})\end{matrix}$ determining an admittance matrix Y by the followingequation:Y _(w)=√{square root over ( A ₂₁ A ₁₂ ⁻¹)}={y _(km) }k,m=l,n ;and  (III) determining a resistance and a reactance of the dipoles(Z_(km), Z_(kk)) by the following equations: $\begin{matrix}{Z_{k,m} = \left\{ \begin{matrix}{{- \frac{1}{y_{k,m}}},{k \neq m},} \\{{1/{\sum\limits_{i = {1:n}}^{\;}\; y_{k,i}}},{k = {m.}}}\end{matrix} \right.} & {({IV})\;}\end{matrix}$
 12. The damping device according to claim 1, furthercomprising: an inductive isolator device connected to the cable.